1. Field of the Invention
The present invention relates to semiconductor manufacturing field, more particularly, to a process of forming a charge storage electrode to which a selective hemispherical grains (HSG) silicon film is applied.
2. Background of the Invention
In general, there exists a problem in that a capacitance of more than certain amount must be maintained to secure operational characteristics of a semiconductor device regardless of the fact that an area of unit cell is reduced as degree of integration of semiconductor device such as DRAM, etc. is increased.
To solve such problem, charge storage electrodes of a variety of 3-dimensional structures were proposed and attempts were made to secure a surface area of the charge storage electrode, however, there were problems in that the process of forming the charge storage electrode involves a high degree of difficulty and induces a large step after completion of the process so as to make subsequent processes difficult. In another scheme of solution, attempts were made to secure the capacitance by using a high dielectric material such as Ta.sub.2 O.sub.5, (Ba.sub.1-X Sr.sub.X) T.sub.1 O.sub.3 (referred to as BST), etc., however, there was a problem in that mass production was difficult since there were many insufficiencies related with processes to be solved to be applied to actual devices.
Recently, a technology for applying the hemispherical grains silicon film to the charge storage electrode has been proposed. This technology can be applied to a high integration semiconductor device of more than 256 mega class since it can increase the surface area of film by more than twice by indenting the surface of film by using a fine structure characteristics. A conventional process for forming the charge storage electrode having the hemispherical grains silicon film includes a process of growing the hemispherical grains silicon film on top of the entire structure of wafer to which a charge storage electrode contact hole is formed, a doping process, deglaze process and etch back process, however, there is a problem in that the productivity is reduced due to the increase of the number of processes, the occurrence of particle, etc..
To solve such problem, a technology for applying a selective HSG process in which the HSG silicon film grows only in a charge storage electrode formation region were proposed. This technology inevitably requires a dry etching process in a patterning process for defining the charge storage electrode and it was confirmed that kind of gas used in the dry etching process acts as a critical parameter which determines a selectibility of subsequent selective HSG process and size of grain. In particular, in case of using carbon halide gas (for example, C.sub.2 F.sub.6, CF.sub.4, CHF.sub.3, CCl.sub.4, etc.), there are problems in that the HSG silicon film is not formed, or even if formed, it can not obtain an effect of expanding the surface area of the charge storage electrode since the grain size of HSG is very small. This is because carbon(C) component, contained in the carbon halide gas which is the dry etching gas used in patterning the charge storage electrode, acts as an element which obstructs the formation of a necessary for formation of HSG silicon film by remaining after the etching process in an amorphous silicon film surface and an interlayer insulation film in which the HSG silicon film is to be selectively formed or obstructs surface migration of silicon atom after formation of seed.
The accompanying FIGS. 6a and 6b show Scanning Electron Microscope(SEM) photographs of a charge storage electrode having a selective hemispherical grains silicon film of simple stack structure formed according to the conventional technology described above. Condition of HSG silicon film growth in the top surface of charge storage electrode can be seen in FIG. 6a and that in the side surface of charge storage electrode in FIG. 6b. As shown in FIG. 6b, the side surface of charge storage electrode is less affected by carbon component during etching so as to show some degree of grain size of HSG silicon film, however, as shown in FIG. 6a, the top surface of charge storage electrode is affected by carbon component contained in carbon halide gas which is the dry etching gas so as to show unsatisfactory growth of grain of HSG silicon film.